This invention relates generally to migration imaging systems and more specifically, to a process of reversal migration imaging whereby an imaged migration imaging member may be fabricated.
A migration imaging system capable of producing high quality images of high density, continuous tone and high resolution has been developed. Such imaging systems are disclosed in copending U.S. applications Ser. No. 837,780 now U.S. Pat. No. 3,975,195 and Ser. No. 837,591 now U.S. Pat. No. 4,013,462, both filed June 30, 1969, both of which the entire contents of which are hereby incorporated herein by reference. In a typical embodiment of these migration imaging systems, an imaging member comprising a substrate, a layer of softenable material containing electrically photosensitive migration material is latently imaged, e.g., by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation, such as light. When the photosensitive migration material is originally in the form of a fracturable layer located at the upper surface of the softenable material, particles of the migration material in the exposed areas of the migration member migrate toward the substrate when the member is developed by decreasing the resistance of the softenable layer sufficient to allow migration of the migration material in depth in the softenable material.
Various methods for developing, i.e., reducing the resistance of the softenable material to migration of the migration material, the latent image in migration imaging systems are known. These various development modes include solvent wash-away and softening the softenable material, e.g., by solvent vapors softening, heat softening and combinations thereof, as well as other methods of reducing the resistance of the softenable material to allow migration of the migration material in depth in the softenable material.
In the solvent wash-away development method, migration material migrates in imagewise configuration in depth in the softenable layer as the softenable layer is dissolved, leaving an image of migrated particles corresponding to the desired image pattern on a substrate, with the softenable layer and umigrated migration material substantially completely washed away.
The imaging system disclosed in copending application Ser. No. 460,377, filed June 1, 1965 now U.S. Pat. No. 3,520,681, the entire contents of which is hereby incorporated by reference, generally comprises a combination of process steps which include forming a latent image on a migration imaging member and developing with solvent liquid or vapor or heat or combinations thereof to render the latent image visible. In certain methods of forming the latent image, nonphotosensitive or photosensitively inert, fracturable layers and particulate material may be used to form images, as described in copending application Ser. No. 483,675, filed Aug. 30, 1965 now U.S. Pat. No. 3,656,990, the entire contents of which is hereby incorporated herein by reference, wherein a latent image is formed by a wide variety of methods including charging in imagewise configuration through the use of a mask or stencil; first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic reproduction techniques and then transferring this charge pattern to the imaging member by bringing the two layers into very close proximity and utilizing breakdown techniques as described, for example, in Carlson, U.S. Pat. No. 2,982,647 and Walkup, U.S. Pat. Nos. 2,825,814 and 2,937,943. In addition, charge patterns conforming to selected, shaped electrodes or combinations of electrodes may be formed by the "TESI" discharge technique as more fully disclosed in Schwertz, U.S. Pat. Nos. 3,023,731 and 2,919,967 or by the techniques discribed in Walkup, U.S. Pat. Nos. 3,001,848 and 3,001,849 as well as by electron beam recording techniques, for example, as disclosed in Glenn, U.S. Pat. No. 3,113,179.
Once a migration imaging member has been developed, i.e., the resistance of the softenable material reduced sufficiently to allow migration of the migration material in depth in the softenable material, and the migration material has, in fact, migrated, then there is no known technique for erasing this image.
There has recently been discovered a system which overcomes this problem of erasing imaged migration imaging members.
Furthermore, the fabrication of layer configuration migration imaging members, i.e., the placing of the migration layer material on or embedded in the surface of the softenable material, has been accomplished by various techniques which include dip coating, roll coating, gravure coating, vacuum evaporation, and other techniques. However, the instant invention overcomes many of the disadvantages of forming, i.e., fabricating, layer configuration migration imaging members by the use of reversal migration imaging.